The invention relates to a medical examining apparatus for the production of transverse sectional images of an exposed object, comprising a ray measuring instrument including a ray source which generates a bundle of rays which penetrate the exposed object, and a radiation receiver which detects the radiation intensity beyond the object by detecting the projected bundle of rays. A driving device for the measuring instrument may comprise a pivot mounting for producing rotational movement of the measuring instrument, and a measurand converter may be provided for converting the signals supplied by the radiation receiver into a sectional image. The compensating body is interposed between the ray source and the radiation receiver and is made of tissue-equivalent material. This compensating body is provided with a patient-receiving through-aperture for enabling a patient to be introduced into the aperture and to be moved through the aperture as a desired transverse body segment is selected for examination.
For determining the sectional image, the rotational movements of the ray measuring instrument may take place through small equidistant angular amounts, each in alternating sequence with a displacement of the measuring arrangement along a straight line perpendicular to a central ray path of the ray beam when a single detector is employed as the radiation receiver. Alternatively, the displacements may be omitted if the ray receiver is built up of a multiplicity of ray detectors, the signals of which are simultaneously registered and processed by the measurand converter. In this case, an X-ray beam of a fan shape may be utilized with the X-ray energy simultaneously incident on all of the detectors which may be arranged in an arcuate array.
An X-ray apparatus of this general type is described in German OS No. 1,941,433. The path followed by the X-ray beam through the object to be examined is here longer at the center of the object to be exposed than in the peripheral regions, owing to the form of most objects which are exposed. Assuming that the object to be examined has constant density, different output signals are obtained from the radiation receiver during scanning which makes the processing of the measurand data difficult. In addition when a polychromatic ray spectrum is employed as is generally the case in medical X-ray diagnostic apparatus, it is found that, owing to varying attenuation of the X-ray beam due to the density differences within the body, the spectral composition of the radiation varies in dependence upon the attenuation. This makes the production of images very difficult.
In order to compensate for the attenuation differences produced between the cetral and peripheral regions owing to the form of the object exposed, it is known from the aforesaid publication to provide a compensating body consisting of tissue-equivalent material having an aperture for receiving the patient and to fill the space between the patient and the compensating body by a waterfilled bag. As this bag is filled, it bears against the outer surface of the patient and conforms to the body contour. In this way, it is ensured that the path of the radiation from its entrance into the compensating body until its exit therefrom is equal in all positions of the measuring arrangement and that, assuming that the object being examined is of constant density, the radiation is equally attenuated in each position of the measuring arrangement. In addition, the water pressure ensures that the patient is kept steady during examination.